2 - Development of Static High-Pressure Techniques and the Study of the Earth’s Deep Interior in the Last 50 Years and Its Future

Summary

Development of static high-pressure techniques over the last 50 years is reviewed from the perspective of the study of the Earth’s deep interior. Fifty years ago, laboratory high-pressure and -temperature experiments were limited to the conditions corresponding to that of near the surface of the Earth. In high-pressure mineral physics, extension of the pressure range directly made possible the study of deeper parts of the Earth, and many scientists spent great effort to improve various experimental techniques. As a result, currently it is possible to do precise X-ray experiments at the conditions corresponding to the center of the Earth: 6,400 km depth from the surface, about 360 GPa, and more than 5,000 K. Two quite different types of high-pressure apparatus are widely used these days. One is the large-volume high-pressure apparatus, and the other is the diamond anvil cell. Although the latter has the advantage of covering wider pressure and temperature conditions together with optical access to the sample, the former has the advantage of much larger sample volume, and, using internal resistance heaters, very stable and uniform high-temperature conditions can be achieved. Many different types of experimental techniques are combined with these high-pressure devices, and rich information about various properties of minerals and melts can now be obtained. Advancement of synchrotron radiation played a key role for such studies, and our knowledge about the Earth’s deep interior has increased considerably. Further efforts are continuing to extend the pressure range beyond the limits of existing high-pressure devices.